-- round trip
SELECT 'E01000001'::gsscode::text;
   text    
-----------
 E01000001
(1 row)

SELECT 'K02000001'::gsscode::text;
   text    
-----------
 K02000001
(1 row)

SELECT 'w00000001'::gsscode::text;  -- lowercase normalised to upper
   text    
-----------
 W00000001
(1 row)

-- is_valid
SELECT is_valid('E01000001');
 is_valid 
----------
 t
(1 row)

SELECT is_valid('E0100000');    -- too short
 is_valid 
----------
 f
(1 row)

SELECT is_valid('E010000011');  -- too long
 is_valid 
----------
 f
(1 row)

SELECT is_valid('101000001');   -- no leading letter
 is_valid 
----------
 f
(1 row)

SELECT is_valid('EA1000001');   -- non-digit in type
 is_valid 
----------
 f
(1 row)

SELECT is_valid('E01999999');   -- reserved code: still valid syntax
 is_valid 
----------
 t
(1 row)

-- invalid input raises
SELECT 'E0100000'::gsscode;
ERROR:  cannot parse input for type gsscode
LINE 1: SELECT 'E0100000'::gsscode;
               ^
HINT:  expected 9 characters: 1 letter followed by 8 digits, eg "E01000001"